
Book _ iBl^.!!/! 




UNITED STATES DEPARTMENT OF AGRICULTURE 




jn-^^wt. 



BULLETIN No. 1028 



Contribution from the Bureau of Entomology 
L. O. HOWARD, Chief 




Washington, D. C. 



PROFESSIONAL PAPER 



March 13, 1922 



APANTELES MELANOSCELUS, AN IMPORTED PARASITE 
OF THE GIPSY MOTH. 

By S; S. Ceossman,' Entomological Assistant, Gipsy Moth and Brown-Tail Moth 

Investigations. 



CONTENTS. 



Page. 

Introduction 1 

Part I. — Description and life his- 
tory 2 

History 2 

Distribution in Europe 3 

Description of species 3 

Methods used in biological work- 4 

Life history 5 

Seasonal history 11 

Feeding of parasitized larva» 

versus nonparasitized larvse 12 

Longevity experiments 12 

Hosts of A. mclanoscelus 12 

Part II. — Introduction and estab- 
lishment 14 

European work 14 

Comparison of seasonal history 

in Sicily and New England 15 



Page. 



Part II. — Introduction and estab- 
lishment — Continued. 

Abundance of A. melanoscelus 

in Sicily 15 

Secondary parasitism in Sicily_ 16 

Colonization in New England 16 

Methods used to obtain material 

for colonization 18 

Success of colonies and distribu- 
tion of A. melanoscelus 21 

Dispersion 22 

Secondary parasitism 23 

The value of A. melanoscelus as 

a gipsy moth parasite 23 

Abundance of A. melanoscelus in 

New England 24 

Conclusion 25 



INTRODUCTION. 

From the year 1905 to December 1, 1911, the State of Massachu- 
setts and the Bureau of Entomology, United States Department of 
Agriculture, shared the expenses involved in cariying on an investi- 
gation of the natural insect enemies of the gipsy moth {Porthet'i'ia 
dispar L.) and the brown-tail moth {Eicproctis chrysorrhoea L.) in 
Europe and of the introduction of parasites of these insects from 

1 The writer wishes to acknowledge the efforts of all those who have been connected with 
the Gipsy Moth Laboratory during the period covered by this report, who have assisted at 
various times in gathering and recording some of the data from which this Ijulletin has been 
prepared. H. A. Preston and C. E. Hood took most of the photographs and W. N. Dovener 
made the drawing of the adult Apanteles. He wLshes especially at this time to express 
his appreciation and thanks to A. F. Burgess, who has general direction of the work, 
for his help and suggestions. 
73070°— 22 1 



2 BULLETIN 1028, U. S. DEPARTMENT OF AGEICULTURE. 

their native homes to New England. A comprehensive report^ of 
this work from its beginnings through 1910 has been published in 
Bulletin 91 of the Bureau of Entomology. 

Among the imported parasites which are now established is 
Afanteles melanoscelus Ratz., a double-brooded parasite of the 
gipsy moth. The following report has been prepared in two parts: 
Part I contains the description of the species and its life historj^, 
and Part II takes up its introduction and establishment. 

PART I.— DESCRIPTION AND LIFE HISTORY. 

HISTORY. 

The insect was described by Ratzeburg^ in 1844 very briefly as 
follows (translation) : 

Microgastcr ntelanoscelu<s is so similar to solitarius that, since it also has 
the same mode of life, one might regard it as merely a variety of that species ; 
but it is distinguished not only by the very black femora. . . but also by the 
third abdominal segment being scarcely rugose, only coarsely punctate at base. 
Pits at the base of the scutel very narrow. The one male which I possess is 
only one line long. 

In 1852 Ratzeburg* again mentions this species and gives a 
record of its being reared from Porthetria dispar L, and StilpTiotia 
solids L. 

Reinhard ^ writes in 1880 as follows : 

The specimens called by Ratzeburg (Ich. der Forstinsect. Ill) Apanteles 
melaiioscelus, bred from Liparis salicis, are beyond all doubt this species. 

Reinhard is here speaking of -4. soUtaHus and believes the two 
to be synonymous. In the same article he places Ratzeburg's type of 
A. melcvnoscelus in A. difflcilis (Nees) Reinh. This is undoubtedly 
incorrect, as the biology of the two parasites is very different. 
Marshall ^ writes in part as follows of A. difficilis: 
Common. The cocoons are flesh-colored or buff . . . ; a few, by some accident, 
are more yellow. The maggots, on leaving the body of their victim, make 
separate naked cases, without clustering together. From 1 to 20 issue from a 
single caterpillar, according to its size. 

Dalla Torre ^ in 1898 also considered melanoscelus synonymous 
with A. diificilis (Nees) Reinh. 

^ How.\RD, L. O., and Fiske, W. F. the importation into the united states of the 

PARASITES OF THE GIPSY MOTH AND THE BUOWN-T.UL MOTH. U. S. Dept. Agr. Bur. Ent. 

Bul. 91. 344 p., 74 flgs., 27 pi. (1 coL). 1911. 

3 Ratzeburg, Julius Theodor Christian, die ichneumonen der forstinsecten, 
V. 1, p. 74, no. 21. 1844. 

* Ratzeburg, Julius Theodor Christian, die ichneumonen der foestinsecten, 
V. 3, p. 56, no. 51. 1852. 

bReinharDj H. beituage zur kenntnis einiger braconiden-gattungen. In Deutsche 
Ent. Zoitschr., jhrg. 24, heft 2, p. 352-370. 1880. 

" Marshall, T. A. monograph of British braconidae, Pt. 1. In Trans. Ent. Soc. 
London, 1885, p. 163. 

' Dalla Torre/c. G. de. oatalogus hymexopterorum, v. i, braconidab, p. 168. 1898. 



LIBRARY D^^NQHESB 



APAXTELES MELAXOSCELUS GIPSY-MOTH PAPiASITE. 



DISTRIBUTION IN EUROPE. 

Apanteles melanoscelus is probably present over most of Europe. 
Specimens have been received at the Gipsy Moth Laboratory from 
Vienna, Austria; Sicily, Italy; Bendery, Russia; and from Saxony, 
Brandenburg. Pomerania, and Rhenish Prussia, Germany. 

DESCRIPTION OF SPECIES. 

It is evident that soUtarius and melaiwscelus are closely related, 
and in time it may be shown that they are the same. If such should 
prove to be the case, the name melanoscelus would have to go, as 
solitariits has the priority. For the present they are to be considered 
as distinct species, and as Ratzeburg's ^^ description of A. melanoscelus 
is very meager, the following new description has been prepared.® 

Female. 

Length 3 mm. Face feebly shagreenecl and strongly sliiny. with a weak 
median welt below insertion of antennae ; vertex, temples, and cheeks shagreened, 
pilose, shiny ; mesoscutnm shallowly, sometimes Indistinctly punctate and shiny ; 
scutellum with the disk very slightly convex, smooth, and polished ; niesopleur?e 
smooth and highly polished, with only a few punctures anterioi'ly and below, 
and a conspicuous weakly crenulate depression posteriorly ; propodeum rugose 
except at base, strongly shiny, and with a prominent median longitudinal carina ; 
forewing with stigma large and with the radius very distinctly longer than the 
transverse cubitus ; posterior coxae large, smooth, and shiny, with a conspicuous 
flattened area on outer edge at base; spurs of posterior tibiiie equal in length 
and about half as long as the metatarsus. Abdomen stout ; entirely shiny ; first 
tergite broader at apex than at base, rugose punctate ; second broad, rectangu- 
lar, more or less roughened, without distinct lateral membranous margins : 
third tergite vrith the rugosity usually confined to the extreme base ; remainder 
of abdomen polished ; ovipositor hardly exserted ; hypopygium not extending 
beyond apex of last dorsal segment. Black; antenna entirely black; tegul.'e 
black ; wings hyaline, the stigma dark brown ; all coxse and trochanters black, 
except sometimes apex of the latter; base of foi*e femora usually, basal half 
of middle femora, and most of the posterior femora black or blackish ; apical 
fourth of hind tibiae and the hind tarsi dusky ; sides and venter of the 
abdomen black. (PI. I, A.) 

Male. 

Essentially as in the female. Differs only in the longer antennae, in the 
usually darker legs, and in the basal abdominal tergites being less roughened. 

The sj^ecies is exceedingly close to A. solifarius Ratzeburg, but 
apparently the differences are sufficiently well marked and sufficiently 
constant to justify holding the two forms distinct. In ^1. solifarius 
the antennae are brownish testaceous toward base, the legs, with the 
exception of the coxse and the basal trochanters, are practically en- 

'^ K.\TzEBtJRG, JuLirs Theodor Christi.w. op. cit. 1844. 

^ The description and translations of references Nos. r! and 5 were made by Mr. C. F. W. 
Muesebeck. 



BULLETIN 1028, U. S. DEPARTMENT OF AGRICULTURE 



tirely stramineous, and the three basal abdominal tergites are more 
coarsely rugose, the roughening on the third tergite extending well 
toward the posterior margin medially ; the narrow lateral mem- 
branous margins on the apical fourth of the first abdominal tergite 
are testaceous in A. solifarius, while they are piceous black in A. 
melanoscelus. 

METHODS USED IN BIOLOGICAL WORK. 

As this species hibernates as a maggot within its cocoon, it is a 
simple matter to gather material during the fall and winter for study 
in the spring. The cocoons were kept in the laboratory yard during 
the winter, in cylindrical cages 3 by 8 inches, made of very fine copper 
netting. Occasionally during the winter a few cocoons were dis- 
sected to ascertain the condition of the maggots and to note any 
changes which might have taken place. As spring approached, the 

cocoons were iso- 
lated, being placed 
in small gelatin 
capsules, or small 
glass vials 1| inches 
by ^ inch. It is nec- 
essary to isolate each 
of the cocoons at 
this time of the year 
for two reasons : 
First, so that one 
may know the exact 
age of the adults 
with which he is 
working and keep the males and females separate; second, to pre- 
vent any secondary j)arasites which may issue from the cocoons 
during the spring from ruining the rest of the xVpanteles material. 
As soon as the Apanteles issued they were removed from their con- 
tainers and placed in glass tubes or glass-covered trays (fig. 1), where 
they were fed a mixture of equal parts of water and honey. A con- 
venient method of feeding is to dampen a small piece of clean sponge 
with the food and place it in the tube or tray containing the Apan- 
teles. The sponge should be washed out every day or so and damp- 
ened again with a fresh mixture of hone}^ and water. 

Parasite-free gipsy-moth larvae were obtained by rearing them 
from eggs, and a supply was kept in trays protected from parasites 
ready for use at all times. 

Two sizes of glass tubes were found convenient, a small one 4 
inches by 1 inch for isolated individuals, and a larger size, 8 by 2 




Fig. 1. — Tray with glass top used in life-history experiments 
with Apanteles melanoscelus. (After Culver.) 



APANTELES MELAXOSCELUS — ^GIPSY-MOTH PARASITE. 5 

inches, for confining several. As the Apanteles are usually active 
and soon exhaust themselves if allowed to remain in the light, the 
tubes or cages containing them were kept dark when not in use. 

Records of oviposition were obtained in the following manner : A 
glass tube containing a single female was brought into the light and 
a parasite-free gipsy-moth larva was introduced on the point of a 
small camel's-hair brush. As soon as the parasite oviposited in the 
caterpillar, the larva was removed to a can for rearing. This pro- 
cedure was continued as long as a female would oviposit readily. 
As soon as she began to show a lack of interest in the gipsy-moth 
larvae, she was returned to the dark to rest and a fresh female given 
an opportunity to oviposit. 

After the first female had rested for an hour or two she was again 
brought into the light and presented with gipsy-moth larvae as 
before. This process was continued with several females throughout 
their life. 

The parasitized larvae were kept isolated in cylindrical cans, 
which measured 2^ by 2 inches, there fed. and kept for future study. 
The structure and length of the various larval instars were determined 
by daily dissections of these parasitized caterpillars. 

LIFE HISTORY. 

Apanteles melanoscelus hibernates as a third-stage maggot within 
its tough sulphur-yellow cocoon. Under field conditions the adults 
emerge from their cocoons over a period of about three weeks. Emer- 
gence is at its height when the gipsy-moth egg hatching is at its 
maximum, usually during the second week in May. The period of 
emergence of adults from cocoons kept at the laboratory where all 
of the cocoons are held under the same conditions is five or six days. 
The majority of the males emerge during the first four days; the 
females, beginning to emerge on the second day, continue emerging 
for four or five days, the bulk of emergence being on the third day 
after the first appearance of either sex. The adult escapes through 
a circular hole which it cuts at the anterior end of the cocoon. 

Females of ^4. melanoscelus are ready for mating or for oviposi- 
tion within two or three hours after issuing. They oviposit just as 
freely whether they have been fertilized or not, and, as is the case 
with many parasitic Hymenoptera, they often reproduce partheno- 
genetically. 

This species does not copulate readily when enclosed in glass vials 
or small cages, but was often observed in coition in the large breeding 
chamber (PI. V, C). The male approaches the female in the usual 
state of excitement with its antennae and wings constantly vibrating. 
The act of copulation is a matter of a few seconds. 



6 BULLETIN 1028, U. S. DEPARTMENT OF AGRICULTURE. 

OVIPOSITION. 

The act of oviposition takes about one second. The female may 
alight upon a gipsy-moth larva from flight or walk up to one. In 
either case the ovipositor is inserted and withdrawn very quickly and 
practically always an individual egg is deposited. Many larvae 
have been dissected after apparent oviposition had been observed 
and in no case has more than one egg been found from a single 
ovijjosition and only rarely have dissections been made which failed 
to show the presence of an egg. Often the larva attacked thrashes 
about so violently that it and the parasite fall, but rarely does the 
parasite fail in its object. After ovipositing in a larva the female 
usually proceeds to another victim, but occasionally will oviposit a 
second time before leaving the caterpillar. She apparently does not 
examine a prospective host but attacks it whether it has previously 
been parasitized or not. This practice of occasionally placing an 
egg in a parasitized caterpillar is unfortunate as only very excep- 
tionally will more than one maggot develop within a single host. 
The parasite favors the posterior half of the caterpillar for oviposi- 
tion, but will ovi^DOsit in any segment of the body. 

The females of ^i. melanoscelus which issue from hibernating 
cocoons prefer to parasitize the first and second stage gipsy-moth 
larvse but will oviposit successfully in third-stage larvae if they are 
present. When the next or summer generation of adults appear, 
most of the gipsy-moth larvae are in the third stage. This is the 
stage most heavily attacked by this generation, although many 
fourth-stage caterpillars are successfully parasitized. Apanteles 
females of this generation often attempt oviposition in fifth and 
sixth stage larvae but are not so successful, for they are hindered by 
the long hairs of large larvae. 

There was considerable variation in the number of ovipositions 
different individuals would make. Between 200 and 300 oviposi- 
tions per female were often obtained in these experiments. The 
greatest number of ovipositions secured b}^ a single female of A. 
melanoscelus was 535. She actually had gipsy-moth larvae before 
her for 510 minutes, making these ovipositions a little faster than 
one a minute.^° The parasite was allowed several oviposition periods 
each day and she would parasitize the gipsy-moth larvae as fast as 
they were introduced for from 30 to 60 minutes. The first day the 
periods of oviposition were a little longer than during the follow- 
ing days. This female issued May 23 from its hibernating cocoon, 
but was not given an opportunity to oviposit until May 27, when 

'" This is about as fast as larvie can be introduced and withdrawn by the process used. 
Under more natural conditions, as found in the large breeding chamber, the females were 
often observed to oviposit 6 or 7 times a minute;. 



APANTELES MELANOSCELUS GIPSY-MOTH PARASITE. 7 

the first gipsy-moth larva was introduced. She worked actively 
every time she was allowed to do so each day to and including June 2. 
On the morning of June 3 she was found dead in the tube. A dissec- 
tion showed that her ovaries still contained about 150 mature eggs 
and about 200 eggs in different stages of development. 

From this and other records, together with notes made from dis- 
sections of mature females of A. melanoscelus, it seems safe to as- 
sume that under natural conditions each female is capable of de- 
positing in the vicinity of 1,000 eggs. 

Egg. 

The egg at time of deposition averages 0.55 mm. in length and 0.1 
mm. in width. It (PI. I, B) is deposited singly in the body cavity 
just beneath the skin of the host. It is transparent, with the cephalic 
end rounded, the caudal end, which is slightly narrowed, bearing a 
short stock. The chorion appears to be entirely without ornamenta- 
tion. Development within the egg is rapid and the embryo begins 
to show form after 15 to 20 hours (PL I, C). By this time the egg 
has widened a little and is slightly shorter than when first deposited. 
JMany eggs have hatched 48 hours after deposition. Just before 
hatching, the fully developed embryo is plainly seen, often in the po- 
sition illustrated in Plate I, D. At this time the egg measures 0.7 
mm. in length and is greatly swollen around the area which incloses 
the head. On one occasion an egg, which was ready to hatch, burst 
while under observation and the larva floated out as illustrated in 
Plate I, E, after which the eggshell shriveled up considerably. 

The length of the egg stage is from 48 to 72 hours, depending on 
the temperature. If the weather is warm, the majority of the eggs 
hatch in about two days. 

Lakva. 

FIRST-STAGE LARVA. 

The following measurements are the average for newly-hatched 
larvae : Total length, 0.7 mm. ; width of head, 0.2 mm. ; width of body, 
0.1 mm. ; length of caudal horn, 0,1 mm. 

The freshly-hatched larva (PL I, F) is found free in the body 
cavity. Directly after hatching it may be found in almost any part 
of the cavity, depending on the point of deposition of the egg. After 
a few hours it works its way to the dorsal part of the posterior third 
of the host and usually remains in that area until about ready to issue 
as a third-stage maggot. 

The larva is transparent and extremely delicate, with a large head 
which is twice the width of the body. The head is composed of a 
single segment. The labium, labrum, and maxillse are present. The 



8 BULLETIN 1028, U. S. DEPARTMENT OF AGRICULTURE. 

sickle-shaped mandibles (Pi. I, J), which are well fitted for tearing, 
are plainly seen, beino; in motion much of the time, as the maggot 
feeds on the lymph and fat bodies of its host. They are 0.08 mm. 
long, are chitinized throughout, but more heavily ^o at the tips, and 
form a good character for distinguishing this stage from the follow- 
ing ones. The body is made up of ten segments at this period, but 
later has eleven after the tenth segment divides. On the dorsum the 
maggot has a sj'stematic arrangement of short, rather stiff, back- 
ward pointing spines. The spines are located as follows : Two each 
on the second and third segments, four on the fourth segment, six 
each on the fifth to ninth segments inclusive, and eight on the tenth 
segment. It seems likely that these spines assist the maggot in 
working itsiway to the caudal end of the host. 

The anal vesicle, which is common to the microgasterine larvae, 
is prominent and the caudal horn is seen just beneath the evaginated 
anal vesicle. 

As the larva matures, the heart, nervous system, and silk glands 
can be distinguished, but no evidence of the tracheal sj^stem is ap- 
parent. 

When read}^ to molt the larva has increased in length to nearly 
2 mm. and the body has widened in proportion, except the head, 
which remains about the same width throughout the stage. 

The larva remains in this stage from two to three days in thfe 
spring generation and from six to eight days in the summer genera- 
tion, 

SECOND-STAGE LARVA. 

In molting the head skin of the first-stage maggot is split off and 
is occasionally found in the body cavity of the host, closely associated 
with the cephalic region of the second-stage larva. The remainder 
of the molt skin is worked back to the last body segment (PI. I, G 
atM). 

The second-stage maggot is usually found dorsally in the caudal 
end of the host in the body cavity, its head toward the posterior end 
of the caterpillar and its body resting longitudinally. When first 
molted it measures about 2.75 mm. in lenglh and 0.55 mm. in width, 
the head and body being approximately the same width. 

In contrast to the first-stage maggot the body is entirely destitute 
of spines and the mouthparts are poorly developed. The mandibles 
(PI. I, K) are not fitted for tearing or biting, but are soft, fleshy 
forms without chitin and are very difficult to locate. 

The anal vesicle is still present and is more prominent than in the 
previous stage (PI. I, G at A). The caudal horn is present but has 
not grown with the developing maggot and appears very small in 
comparison with the size of the larva (PI. I, G at P). 



Eul. 1022, U. S. Dept. of Agriculture. 



Plate 1. 




APANTELES MELANOSCELUS. 

A, adult, female; B, egg, dissected from female; C, egg, after 15 to 20 hours in host; D, egg, after 
4S hours in host; E, first-stage larva and shriveled eggshell from wiiich it came, 50 hours 
after oviposition; i?", first-stage larva; G, second-stage larva; tt?, molted skin, /), caudal horn, 
a, anal vesicle; IJ, third-stage larva, dissected from host; a, anal vesicle; /, third-stage larva, 
hibernating form, dissected from cocoon; J, first-stage larval mandible; K, second-stage larval 
mandible: L, third-stage larval mandible. All much enlarged. 



Bui. 1028, U. S. Dept. of Agriculture. 



Plate II. 




APANTELES MELANOSCELUS. 

A, Hibernating cocoons on b(iard found in Molro.se, Mass., 1917; B, first-generation cocoons on 
brancii collected at Quincy, Mass., 1920; C, first-generation cocoons on branch collected at Mel- 
rose, Mass., 191G; D, first-generation cocoons on branch collected at Qnincy, Mass., 1920; E, 
third-stage maggot two-thirds of its way out of fourth-stage gipsy-moth larva; F, third-stage 
maggot dissected from host, anal vesicle still evaginated. 



3ul. 1023, U. S, Dept. of Agriculture. 



Plate III. 




APANTELES MELANOSCELUS. 

.1, Hibernating cocoons on underside of vessel collected at Wevmouth, Mass., 1920; B, hiber- 
nating cocoons on underside of bark collected at West Bovlstbn, Mass., 1920; C, hibernating 
cocoons on underside of branch collected at Hinghain, Mass., 1920; D, hibernating cocoons 
on stump collected at Melrose, Mass., 1916. 



APANTELES MELANOSCELUS GIPSY-MOTH PARASITE. 9 

The heart, nervous system, and silk glands are more pronounced, 
especially the latter, which are coiled and recoiled and appear to fill 
mucli of the body cavity. Traces of the tracheal system are observed 
during the last part of the stage. 

Development is rapid and in two or three days the maggot has 
increased in size to 4.5 mm. long and 1 mm. wide. 

The average period spent in this stage by the first- generation larva 
is from two to three days and for the second generation from five to 
seven days. Just before molting the mandibles of the third-stage 
maggot can be seen. 



THIED-STAGE LARVA. 



The period spent by the third-stage maggot (PI. I, H) within its 
host varies from a few hours to two days with the spring generation 
and as long as three days with the summer generation. When a 
second-stage maggot is about ready to molt it usually works its way to 
the central part of its host and molts there, although occasionally 
third-stage larvae are found in the caudal end of the caterpillar. Just 
before issuing the maggot is 5 to T mm. long, is slender, and tapers 
toward the anterior end ; it is dull white and dorsally is sparsely cov- 
ered with very fine, inconspicuous hairs. At the caudal end of the 
body the aiial vesicle is still evaginated (PL I, H at A; PL II, F). 
The body is apparently filled with the silk glands and has, a well- 
developed tracheal sj^stem, with eight pairs of spiracles visible. There 
is a pair on the second segment and a pair on each of segments 4 to 
10, inclusive. The spiracles are very tiny and difficult to determine, 
the last seven pairs being associated with laterally protruding areas. 
On the eleventh segment there is a slight protruding area laterally 
which may contain a spiracle, but one was not observed on this seg- 
ment. The mouthparts are plainly visible, consisting of labium, 
labial palpi, labrum, maxillae, maxillary palpi, and mandibles. The 
mandibles (PL I, L), which are 0.26 mm. long, are strong and well 
fitted for tearing. They are slightly curved anterio^l3^ The tip is 
divided into two sharp teeth. The anterior third of the mandible 
appears to be double with two biting edges, each edge armed with 
several teeth. There are dorsally on this part of the mandible two 
elevations which appear to strengthen the organ. The tips and points 
of the teeth are more heavily chitinized tlian the rest of the mandible. 

When ready to issue the maggot tears a hole in the side of the 
caterpillar, usually in the fifth or sixth segment. When it has issued 
to about two-thirds its length it begins to form its cocoon (PI. II, E). 
By the time the larva is entirely out, the anal vesicle has been in- 
vaginated. If the larva is of the spring generation, it voids the 
accumulated waste material of the larval stages after 18 to 20 
hours in the cocoon. In about two days after completion of the 
73070°— 22 2 



10 BULLETTlSr 1028, U. S. DEPARTMENT OF AGRICULTURE. 

cocoon the maggot pupates and casts its larval skin, which is pushed 
back to the posterior end of the cocoon over the previously voided 
material. 

The third-stage maggot (PI. I, I) of the summer generation has 
quite a different cycle. After having completed its cocoon, in which 
it is to hibernate, it becomes shorter and stouter, measuring about 
4 mm. in length. It is a pale lemon yellow, and remains quiescent 
until the following spring. About the time when the first gipsy 
moth eggs hatch, the maggot resumes activity, first voiding the ac- 
cumulated waste in the caudal end of the cocoon. Two or three days 
later pupation takes place, and the larval skin is cast and pushed to 
the caudal end of the cocoon, as in the spring generation. 

Pupa. 

The pupal stage lasts from five to nine days. About two days after 
the completion of the cocoon the larval skin is cast. The pupa is 
whitish with long appendages and has a movable abdomen. The 
eyes soon begin to darken, the ocelli are distinguishable, and the 
thoracic and abdominal segments take form. The mouth parts, an- 
tennae, legs, and recurved ovipositor are plainly seen. In three or 
more days the development is complete. The whole is now dark, 
nearty black. The pupal skin is cast and the adult lifts the cocoon 
cap, having cut around its base, which was left weak by the spinning 

larva. 

Cocoon. 

When the third-stage maggot is about two-thirds of its way out 
of the host, it begins to construct its cocoon. The first few threads 
seem to be attached ventrally to the maggot itself on the last seg- 
ment which is outside of the caterpillar. After making an attach- 
ment at this point the maggot straightens out horizontally, then 
swings back underneath itself again and makes another attachment. 
It continues this process laterally and dorsally, spinning all the 
while and forming loops which it gradually fastens securely in a 
similar manner. As the outer loose cocoon is developed, the maggot 
must break away from the original attachments and gradually work 
itself entirely free from its host. The maggot reverses its position 
several times during the construction of the cocoon. When com- 
pleted, the cocoon is about 5mm. long and is composed of an outer 
loose covering of fine threads, some of which are attached to the 
host or any object on which it may rest. Just within this is a tough, 
tightly woven envelope, which encases a very fine smooth inner sac 
next to the maggot. The cocoon is slightly flattened on its ventral 
surface and convex laterally and dorsally. The anterior end is 
rather flat. The cap, which is thinner along its base, is at the ante- 
rior end. The posterior end is slightly pointed. It takes the spring- 



APANTELES MELANOSCELUS GIPSY-MOTH PARASITE. 11 

generation maggot about two hours, to form its cocoon and the sum- 
mer maggot three to four hours to complete the cocoon in which it 
is to hibernate. 

The cocoon made by the spring-generation maggot is pale yellow- 
ish white, a little smaller and rather delicate as compared with the 
hibernating cocoon, which is a light sulphur yellow and very tough. 

LOCATION OF COCOONS. 

The cocoons of the spring generation are found singly or in 
clusters, depending upon the degree of gipsy moth infestation and 
the abundance of Apanteles. In low growth the cocoons are very apt 
to be found on the foliage and often on the debris on the ground, 
as well as along the trunk and small branches. On large trees a few 
cocoons are found on the foliage, but if abundant the majority are 
located at the junction of the smaller brandies on the underside. 
The cocoons are attached lightly, often on top of others and in- 
variably a dead second-stage gipsy moth larva is found with each 
cocoon (PI. II, B, C, D). After the adults have issued these cocoons 
are easily washed or blown from the trees and are seldom found the 
next spring. 

The second-generation cocoons are found securely attached scat- 
teringly over the tree trunk and in clusters under the larger limbs 
where the gipsy-moth larvae congregate. These cocoons are not 
often foimd on the foliage. 

The gipsy-moth larvae, when parasitized by the second generation 
of Apanteles Tnelanoscelus^ have a tendency to crawl to protected 
and out-of-the-way places just before the issuance of the parasite 
maggots. The cocoons are often associated with the gipsy-moth 
pupse and larger caterpillars. They are found behind billboards 
and signs, attached to trees (PI. Ill, D). on the undersides of 
boards on the ground (PI. II, A), under fence rails or rocks, under 
loose bark, and on rough surfaces on the underside of limbs (PI. 
Ill, B, C). Plate III, A, shows a tin vessel found during the sum- 
mer of 1920 in a dump at Weymouth, Mass., and illustrates the 
habit of parasitized larvae of crawling to hidden places. There are 
a few over 100 cocoons on the bottom of this vessel, and there is a 
cluster of 25 cocoons on one side of the vessel not shown in the 
photograph. 

SEASONAL HISTORY. 

The seasonal history varies considerably with the season. The is- 
suance of adults of Apanteles melanoscelus from their hibernating 
cocoons begins about the time of maximum hatch of the gipsy-moth 
eggs, which is usually near the middle of the second week in May. 
During such a season most of the Apanteles will have issued by May 
20. Under field conditions females of Apanteles melanoscelus do not 



12 BULLETIN 1028, V. S. DEPARTMENT OF AGRICULTURE. 

begin to oviposit immediately, for the bulk of issuance of the spring 
generation parasite maggots is around June 12. The adults which 
develop from these maggots will be found issuing from 7 to 11 days 
later. Cocoons of the second generation, or those in which the para- 
site is to pass the winter, begin to appear about the fourth of July, 
but usually not in abundance until the second week in July. 

FEEDING OF PARASITIZED LARV^ VERSUS NONPARASITIZED LARV^. 

Several feeding records were kept of gipsy-moth larvae which were 
known to be parasite-free as checks against similar feeding records 
of larvae in which A. melanoscelus had oviposited. The records show 
that healthy gipsy-moth larvae eat from two to three times as much 
as those which contain parasite maggots. These data were obtained 
from feeding records made during the period between oviposition in 
the caterpillar and issuance of the parasite maggot and the checks 
were kept only for a similar number of days. The gipsy-moth larva 
from which a maggot of A. melmioscelus has issued eats no more, al- 
though it may live a few hours or as long as two weeks, the average 
being seven days. 

LONGEVITY EXPERIMENTS. 

The tray shown in figure 1 (p. 4) was found most satisfactory for 
the longevity experiments although glass tubes 8 by 2 inches were 
used successfully for small numbers of parasites. 

The adults were fed on an equal mixture of honey and water, 
sprayed on small pieces of sponge. It is important that the sponges 
should be kept clean by thoroughly washing every other day. 
Nothing but the food was inclosed in the trays with the adults, but 
in the tubes they did better if a crumpled bit of paper was present 
on which the parasites might rest and clean themselves. A. melanos- 
celus in the tubes and trays, if kept in the light, lived for about one 
week. When the containers were kept darkened by means of black 
paper, the parasites remained rather inactive much of the time, and 
lived considerably longer. 

In several experiments with adults issuing in spring and summer, 
males and females lived for 30 to 32 days. In one case a female of 
the summer issuing generation lived 35 days. There was very little 
difference in the length of life of the adults, the females living 
slightly longer than the males. Without food they were able to live 
only a few days. 

HOSTS OF A. MELANOSCELUS. 

Ratzeburg" gives as hosts in Europe Porthetna dispar L. and 
Stilpnotia sal ids L. 

From field-collected material in this country ^4. melanoscelus has 
been reared only from the gipsy moth. S. salicis, the satin moth. 

^^ RATZEB0RG, Julius Theodor Cheistian. op cit. 1852. 



APAISTTELES MELANOSCELUS GIPSY-MOTH PARASITE, 13 

recorded as a host of this parasite in Europe, was not found in 
America' until the latter part of June, 1920. when a heavy infestation 
was discovered at Medford, Mass. A-VHien the infestation was found 
the larvae were from half to full grown and rather too large to be 
expected to harbor A. melanosceJus maggots. Collections of larvae 
were made immediately, but no A. melanoscelus were reared. On 
several occasions, however, cocoons of this species were found on tree 
trunks closely associated with belated larvae of Sf Up not la solids, and 
there is very little doubt that these cocoons were spun by A. mela- 
noscelus maggots which had issued from the near-by small and 
inactive larvae of S. salicis. It is known that Avith the gipsy moth 
the larvae from which A. melanosceJus maggots issue do not die for 
several days. They are rather inactive and often do not move far 
from the place where they were when the parasite issued. 

In August, 1920, an outbreak of Uemerocampa leucostigma S. & A, 
was located in a small area in Somerville, Mass. This is the first 
time since -1. melanoscelus has been established that larvae of the 
white-marked tussock moth could be collected in eastern Massachu- 
setts, except ver}^ sparingh'. The season was too far advanced to 
expect to rear A, melanoscelus from collected material, and none were 
recovered from larvae brought to the laboratory. It was apparent, 
however, from observations made at the infestation, that this parasite 
had been responsible for the untimely death of very many tussock- 
moth larvae, for the cocoons of -4. melanoscelus Avere abundant on 
the sheathing of near-by houses Avhere the tussock-moth larvae had 
gathered in large numbers and were spinning their cocoons. 

Several experiments were tried confining adults of .1. melanoscelus 
with various larvae. Reproduction w£^s successful with M alacosoma 
americana Fab., BI. disstna Hiibn., Hemerocampa leucostigma S. & 
A,, Olene hasiflava Pack., and Euproctis chrysorrhoeal^. The female 
attacked all but the last eagerly. Oviposition apparently took 
place in Charidryas nycteis D. & H., Hemileuca niaia Dru., Pteronus 
ribesii Scop., and in a species of tortricid. All of these larvae died 
and were dissected. Several maggots of A. melanoscelus were found 
in the larvae of C. nycteis^ but no evidence of parasitism was found in 
the other larvae. 

Several larvae of Stilpnotia salicis were presented to females of 
A. melanoscelus. No oviposition was recorded. This was late in the 
season and the larvae had matured much beyond an attractive stage 
for oviposition by this parasite. 

Some six or seven species of smooth-skinned or hairless larvae have 

been confined with females of ^4. melanoscelus but rarely have they 

shown any attention to them. This parasite evidently will attack 

quite a number of small hairy lepidopterous larvae when the oppor- 

73070°— 22 3 



14 BULLETIN 1028, U. S. DEPARTMENT OF AGEICULTITEE. 

tunity presents itself, but shows very little interest in large hairy 
caterpillars or in larvse which are destitute of hair or only 'sparsely 
covered. 

PART II.— INTRODUCTION AND ESTABLISHMENT. 

EUROPEAN WORK.i- 

In January, 1911. Mr. W. F. Fiske, who was at that time in charge 
of the parasite work under the direction of Dr. L. O. Howard, Chief 
of Bureau, sailed for Italy to investigate the parasite situation. The 
main object at that time was to make a study of conditions there and 
to attempt to introduce on a large scale Chcdcis flavipes Panz., a 
pupal parasite of the gipsy moth. Headquarters were located at 
Naples and a vacant building was rented and fitted up for use as a 
laboratory near the School of Agriculture at Portici. 

Early in February, 1911, Mr. Fiske visited several places in Sicily 
to ascertain the field conditions and degrees of gipsy moth infesta- 
tion preliminary to obtaining the Chalcis material. While there he 
discovered that cocoons of a species of Apanteles were present in 
" countless thousands." This came very much as a surprise, and he 
determined to put most of his energies, even at the expense of pre- 
vious plans, into an eifort to send this parasite to America in as large 
numbers as possible. 

The localities, a forest at San Pietro, Caltagirone, and the forests 
back of Barcellona, in Sicily, were situated where the gipsy-moth 
larvae and cocoons were sufficiently abundant to warrant the collec- 
tion of either in large numbers. Both places were some distance from 
a railroad, and the location which gave more promise was the less 
accessible of the two. As soon as the gipsy-moth larvse had hatched 
and were of sufficient size to have been parasitized, collections of 
larvse were begun. A foreman and crew were located at each place, 
and the collections of larvae were started. The first larval collection 
arrived from Caltagirone at Portici on May 14, and a few cocoons were 
present at that time. When the collections arrived at Portici they 
were placed in trays in the house which was rented for that purpose. 
About a dozen Italian girls took care of the trays — ^that is, fed the 
caterpillars, removed the parasite cocoons daily, and kept the trays 
clean. These girls were very adept at this work, being familiar with 
the care of silkworms and having assisted in handling alfalfa weevil 
parasite material for shipment to America. 

As soon as the cocoons were removed from the trays they were 
placed in cold storage to prevent the further development of the 
parasites. 

^'^ The part of this report pertaining to European work is based on the correspondence of 
Mr. W. F. Fiske whll? in Europe. 



APANTELES MELANOSCELUS GIPSY-MOTH PARASITE. 15 

The tray work was supplemented by collections of the cocoons in 
the field and these had to be iced to prevent as much as possible any 
issuance of secondary parasites, as well as to retard the development 
of the maggots of Apanteles melanoscelus. When the cocoons arrived 
at Portici they were usually picked over and repacked, although it 
was not possible to do this in all cases. 

The shipments depended largely on the supply of parasite material 
on hand and the dates of departure of vessels to America ; but the 
j)olicy followed Avas to ship as often as possible. 

Several types of containers were used for transporting the cocoons, 
all of which came in the vessels' cold storage and all proved quite 
satisfactory. One type of refrigerator was so made that the small 
packages of cocoons of Apanteles in the inner chamber were entirely 
surrounded by ice. This refrigerator was a double-walled aifair and 
rather expensive to construct. It was inclosed in a box of sawdust. 
Another type was a sort of ice-cream freezer arrangement consisting 
of two metal water-tight cylinders, one within the other, with the 
cocoons in containers packed in sawdust within the inner cylinder. 
Ice was packed between the two cylinders and the whole was packed 
in sawdust in a large wooden box. At the bottom of the outer cylin- 
der was a small pipe which went through the box and allowed the 
water to drain off. On some occasions the containers were repacked 
with ice in New York before being forwarded to Melrose. A few 
shipments of cocoons which were merely packed in boxes, and kept 
in cold storage for as much of the trip as possible, came through in 
good condition. 

COMPARISON OF SEASONAL HISTORY IN SICILY AND NEW ENGLAND. 

The spring of 1911 was cold, rainy, and rather backward in Sicily. 
By May 15, however, parasite maggots had begun to issue from the 
gipsy-moth larvse. The earliest record for issuance of maggot's for 
New England is May 22. It is likely that during many seasons in 
Sicily maggots issue by May 7, whereas the New England record re- 
ferred to is an early one, issuance of maggots usually beginning the 
last of May. This would make the season in Sicily about three weeks 
earlier than at Melrose Highlands, Mass. The second-generation 
cocoons were being collected in Sicily by June 10, 1911, but June 23 
is the earliest record of the presence of this generation in New Eng- 
land. 

ABUNDANCE OF A. MELANOSCELUS IN SICILY. 

Tlie parasite cocoons were very abundant in places as indicated in 
notes and correspondence received from Mr. Fiske. 

Apanteles killed more caterpillars than all of the other parasites put together. 
Cocoons average 1,000 to a tree, not counting the smaller trees. 



16 BULLETIN 1028, U. S. DEPARTMENT OF AGRICULTURE. 

Notes made at another place state : 

Apanteles exceedingly common. Estimate 75 per cent control on average and 
higher in some places. Estiniate 10,000 cocoons on one large tree. 

To illustrate the abundance of cocoons, those present on an area 
the size of a man's hand were counted and the number found was 
187. Mr. Fiske states that there were more over a similar area high 
up on the tree. The same day he visited another place and found 
conditions similar. 

SECONDARY PARASITISM IN SICILY. 

Apparently the first-generation cocoons are not attacked seriously 
by secondaries, probably less than 10 per cent being killed. Secor J- 
ary parasitism of the hibernating cocoons is very heavy, and one note 
was found referring to a location where it was feared that it Wv^ld 
almost exterminate the parasite. Sometimes as high as 75 per cent 
of the cocoons from Sicily received at the laboratorj^ and wintered 
were killed by secondaries. 

COLONIZATION IN NEW ENGLAND. 

During the rush of the season's work it was supposed that two or 
three species of Apanteles were represented and the importation and 
colonizations were recorded iA correspondence and in the notes as 
A. soJitarius and Apanteles II and III. The confusion was not at 
all surprising for there were two and possibly three species repre- 
sented, but the fact of the matter, as it appears at the present time, 
is that the adults liberated during June, 1911, at North Saugus, Mass.. 
from cocoons imported from Sicily as A. solitarius, were adults of 
the first generation of A. mclanoscelus ; and that the cocoons received 
later in the summers of 1911 and 1912, which were hibernated at the 
laboratory, and the adults from which were liberated at Melrose 
during the springs of 1912 and 1913, were cocoons of the second 
generation of A. mel-anoscelus. 

During June, 1911, about 125,000 cocoons of the first generation 
were received from Europe, and every precaution was taken to pre- 
vent the escape of any secondaries which might be present. As soon 
as they were received at the laboratory they were taken to North 
Saugus, Mass.. and immediately placed in darkened containers from 
which nothing could escape except by entering glass tubes, where 
the}' were inspected, the good allowed to escape and the bad de- 
stroyed. In this manner 23,000 adults were liberated during June 
and July, 1911. During the months of July and August, 1911, 
nearly 17,000 hiberating cocoons were received. These were iso- 
lated at the Melrose Highlands laboratory, each one being placed in 
a small gelatin capsule and then wintered under outdoor conditions. 



>1. 




■^ 5i- -ft *» 



S 



Fold-out 
Placeholder 



This fold-out is being digitized, and will be ir 

future date. 



APANTELES MELANOSCELUS GIPSY-MOTH PARASITE. 



17 



During the spring of 1912 the adults which issued from these cocoons 
were liberated near the laboratory. 

Early in 1912 Mr. Fiske again went to Italy, this time with several 
assistants. As one of the results of this trip, 22,000 cocoons of the 
second generation of .1. itielanoscelus were received during the 
summer of 1912. These cocoons were collected in the forest of San 
Pietro, near Caltagirone, Sicily, during the week beginning June 15. 
They were shipped to Naples in cold storage on June 22 and held 
there in cold storage until all had been isolated in gelatin capsules. 
Early in July they were sent to America in cold storage and hiber- 
nated at the laboratory. The adults which issued in the spring of 
1913 were liberated at Melrose. 

Table 1 shows the number of individuals of A. melanoscelus that 
have been liberated in New England. The colonizations of 1911, 
1912, and 1913 were adults which issued from cocoons received from 
Sicily ; the rest of the colonization material was obtained by rearing 
and breeding New England material. 

Table 1. — Xumber of A. inelanoscclus liberated in Netc England, 1911-1920. 



Year. 


Number 
of adults 
liberated, 
Sicilian 
material. 


Cocoons 
colonized. 

New 
England 
material. 


Number 
of colonies 
placed in 

Massa- 
chusetts. 


Number 
of colonies 
placed in 

New 
Hamp- 
shire. 


Number 

of colonies 

placed in 

Rhode 

Island. 


Total 
number 

of 
colonies. 


1911 


23,000 
203 
273 




1 
1 
1 

2 
11 
7 
9 
2 
11 






1 


1912 








1 


1913 








1 


1915 . . 


i,566 
5,541 
3,500 
8,100 
930 
10, 100 


1 




3 


1916 








11 


1917 








7 


1918 




7 




16 


1919 






2 


1920 -• 




9 


1 


91 








Total 


2;3,476 


29, 671 


45 


17 


1 


63 







As will be seen from a study of the figures in Table 1, very few 
adults were liberated in 1912 from the 17,000 cocoons received in 
1911, and in 1913 from the 22,000 cocoons received in 1912. The 
poor issuance from these imported cocoons was due to several factors. 
Fifty to seventy-five per cent were killed by secondaries and a few 
were injured while being collected. These cocoons were kept in 
gelatin capsules from the middle of the summer until the adults 
issued the following spring. Subsequent experiments have shown 
that the mortality of hibernating larvae of Apanteles melanoscelus 
was not so high when the cocoons were isolated in small glass vials 
plugged with cotton batting as when they were kept in gelatin cap- 
sules. An examination of dead maggots of A. melanoscelus^ which 
had been isolated in gelatin caj^sules, showed that the maggots were 



18 BULLETIN 1028, U. S. DEPARTMENT OF AGRICULTURE. 

very dry and shriveled, and indicated that death might have been 
due to lack of moisture within the capsules. 

No colonies were liberated in 1914, as no importations were made 
and the parasite had not been sufficiently well established to furnish 
colonization material. 

All Apanteles Tnelanoscelus liberated since 1913 have been put 
out while in the cocoon and have been of the summer-issuing 
generation. Most of these colonies have contained 500 cocoons. In 
liberating a colony the cocoons are taken to the field and emptied 
into a small cylindrical can, which is then nailed to a tree in an in- 
conspicuous place. A cover is placed on the can to protect the 
cocoons from rain and birds. The adults escape through three 
:|-inch holes punched in the can near the top. The size of the can is 
not especially important, but a convenient can used at the laboratory 
is 3 inches in height and 2 inches in diameter. It is necessary to place 
a J)and of tree-banding material entirely around the can to prevent 
ants from destroying the colony. 

In selecting sites for colonies, woodland areas with a light to 
medium gipsy-moth infestation are preferable. Heavily infested ter- 
ritory which is apt to be stripped of its foliage should be avoided. 

After the colony has been liberated a roadside tree is marked in 
white paint with an arrow pointing to the colony and the letters A. M. 
In the woodland near the exact spot of the colony a tree is banded 
with white paint. These field marks are made so that the place can 
be found later if desired. At the same time a numbered note is 
written for the laboratory files which explains the condition at the 
colony site and gives directions for finding the colony. 

The colonies have been placed in groups of towns, one colony in 
each town, as shown in the accompanying map (PI. IV). This 
method of liberating colonies was used because the parasite disperses 
rapidly and there was considerable chance that small colonies would 
not become established if they were placed singly at widely separated 
locations. In this way several rather large areas, from which the 
parasite can spread to the surrounding towns, have become well 
stocked. 

METHODS USED TO OBTAIN MATERIAL FOR COLONIZATION. 

The story of the introduction of A. melanosceJus and the colonies 
liberated from the imported material has been recorded earlier in 
this paper. Two methods have been used to get material for coloniza- 
tion since the establishment of the parasite in New England — first, by 
rearing the parasite from field-collected gipsy-moth larvae, and, sec- 
ond, by breeding the parasite at the laboratory. 

The first method consists merely of making collections of large 
numbers of second-stage gipsy-moth larvse from locations where the 
parasite is present in sufficient numbers to warrant such collections. 



APANTELES MELANOSCELUS GIPSY-MOTH PARASITE. 19 

These larvae are placed in trays and fed until the parasite maggots 
issue. The maggots, upon issuing, spin their cocoons, usually attached 
to the caterpillar or to the object on which the host was resting at 
time of issuance. Each day the gipsy-moth larvae are fed, the trays 
cleaned out, and all of the parasite cocoons removed. The cocoons 
are put up in lots of 500 and kept in a refrigerator until they are 
placed in the field. They are colonized as soon after removal from the 
trays as possible, usually on the following day. Occasionally it has 
been necessary to keep the cocoons in the ice chest five or six days, 
and this has been done without any apparent injury to the parasite. 

The second method of securing material for colonization may be 
divided into two parts, namely, the fall work which consists of 
gathering and caring for the hibernating cocoons, and the actual 
breeding work which is carried on in the spring. There is a great 
mortality of wintering A. melanoscelus, largely due to secondary 
parasitism, and a large number of cocoons must be gathered in order 
to have a few adults of Apanteles in the spring to start the breeding 
work. The cocoons are collected as soon as possible after they have 
been found, in an endeiivor to get them before the secondaries or 
ants do. 

From 10,000 to 20,000 cocoons are collected during July from 
places where the parasite is abundant. Some of the secondaries 
present at this time hibernate within the cocoon, but there are many 
which have one or more generations during the early fall. 

For a number of years these cocoons were isolated in gelatin 
capsules as soon as they arrived at the laboratory. This prevented the 
issuing secondaries from doing any further damage, but it was 
found that the spring issuance of A. rrielanoscelus from apparently 
good cocoons was exceedin,gly small. This was due partly to sec- 
ondaries which hibernate within the cocoons, partly to injurjr while 
handling, and considerably to the drying of the maggots of A. 
■melanoscelus in the cocoons. The last two years the cocoons have not 
been isolated, with the result that a better spring issuance has been 
obtained. Instead of isolating the cocoons they were separated into 
lots of 100 each and placed in glass tubes 1 by 4 inches, which were 
plugged with cotton batting. These tubes were then placed on a 
background of white in a warm bright place where they could be 
watched and the secondaries were removed as fast as they issued. 
Most of the secondaries issuing in the summer leave the cocoons with- 
in two weeks after collection, although a few continue to issue for 
two weeks longer. After the secondaries have stopped issuing the 
cocoons are picked over and the empty ones and those showing ex- 
ternal injury are discarded. Many of the cocoons which contain 
hibernating secondaries at this time can be distinguished by a slight 
discolored spot on the cocoon ; such cocoons also are destroyed. The 



20 BULLETIN 1028, U. S, DEPARTMENT OF AGRICULTURE. 

remaining cocoons are placed in bulk in a fine copper-wire cage which 
is nailed in a protected place in the yard until spring. 

The spring work begins during the last of April when the cocoons 
are removed from their hibernating cage and isolated for a short 
period in capsules. They are isolated at this time for convenience in 
handling the adults of Apanteles and destroying the wintering second- 
aries which issue. The cocoons are isolated in the capsules less than 
two weeks before A. rnelanoscelus begins issuing, and this short period 
of confinement does not have a detrimental effect. As the adults 
emerge they are removed hourly from the capsules and placed in 
glass tubes 8 by 2 inches. The sexes are kept separate. A sponge 
dampened with a mixture of equal parts of honey and water is placed 
in each tube. The tubes are then placed in a cool, dark place until 
ready for use. 

Several different types of cages and trays have been tried as breed- 
ing chambers with varying degrees of success. A. inelanoscelMS^ like 
most hymenopterous parasites, is extremely heliotropic and indi- 
viduals are found resting on the sides or top of the container or ex- 
hausting themselves flying about the source of light. During the past 
summer a breeding chamber was devised which eliminated the unsat- 
isfactory light conditions of previous cages (PI. V, A, B, C). This 
type of breeding chamber should prove of value in breeding work 
with other parasites. 

The empty chamber is shown in Plate V, A, resting on one side. It 
is merely a wooden case with a glass bottom and top, with an opening 
left in one end, through which the tray containing the larvse to be 
parasitized is admitted. The opening is just wide enough to allow the 
introduction of the tray and is about 2 inches deeper than the tray. 
Cleats on which the tray is to rest are arranged inside the chamber 
about 2 inches from the bottom. The tray should fit closely to the 
sides and ends of the chamber, but not tightly enough to bind when 
being introduced or removed. After the tray has beqji put in place 
the opening in the end of the cage is closed with a tightly fitting board 
(PI. V,AatX). 

When the chamber is to be stocked with the parasites it is 
placed on a flat surface which has previously been covered with 
black paper (PL V, B). A piece of black paper is laid over 
the top, covering all but 6 or 7 inches of the glass at the end 
of the chamber facing the sun (PI. V, B at L). The parasites 
are liberated in the cage and fly to the uncovered part of the cham- 
ber where they gather on the glass top. The tray containing the 
small caterpillars is slid into place and is shown, part way in, in 
Plate V, B at T. The open end of the chamber is now closed and 
the whole thing is removed to two wooden horses, as shown in Plate 
V, C. A piece of black paper is now placed over the entire top. 



Bui. 1028, U. S. Dept. of Aericultur9 



Plate V. 




APANTELES MELANOSCELUS. 

A . Breeding chamber resting on its sido: j, Board to close open end: B, Chanilier ready I o M ock with 
parasites and siiJsy-moth larvae. Tray containing gipsy-moth larvae shown at t, part way in; 
1 ne light IS admitted at I. C, chamber resting on horses, with liglit entering from bottom only. 



APAISTTELES MELANOSCELUS GIPSY-MOTH PAEASITE, 21 

With this arrangement all of the light entering the chamber comes 
from beneath, through the glass bottom of the chamber and through 
the cloth-covered bottom of the tray. Five minutes after the cham- 
ber is in this position practically all of the Apanteles have left the 
top of the chamber and are found dispersed over the bottom of the 
tray, where the gipsy-moth larvae are feeding and crawling. The 
parasites begin ovipositing in the caterpilla-rs immediately after 
they have been attracted to the bottom of the tray. 

When the caterpillars have been exposed to Apanteles Tnelano- 
scelus for a sufficient period the operations are reversed; the cham- 
ber is placed on a black-covered surface with the end of the cham- 
ber opposite the end where the tray is to be removed, facing the sun. 
Light is now admitted by removing the black paper over a space of 
6 or 7 inches, as shown in Plate V, B at L. In a few minutes most 
of the parasites will congregate in the top of the chamber at the 
light end. The opposite end of the chamber can now be opened 
without danger of any of the parasites escaping. The tray is with- 
drawn slowly, care being taken that all of the Apanteles have left 
it. If any still remain, they will fly to the light end of the chamber 
when disturbed by touching them with a small camel's-hair brush. 

As soon as the tray has been remoA'ed another one is introduced and 
the process is repeated as long as the supply of Apanteles melanoscelus 
lasts. The larvae parasitized in this manner are fed in the trays until 
the parasite maggots issue. The resulting cocoons are removed each 
day for colonization. 

A breeding chamber stocked with 300 adults of Ajjanteles Tiiel^an- 
oscehis, with the sexes equally divided, can be used about one week. 
Each tray should contain about 10,000 first-stage gipsy-moth larvae. 

The period of exposure of the larvae to the parasites varies with the 
temperature and time of day. The parasites are most active during 
the middle of the day. The larvae were enclosed in the chamber about 
two hours during this part of the day. Earlier in the morning and 
later in the afternoon the larvae were exposed for about three hours. 
An average of about 1,000 parasite cocoons were removed from each 
tray. Undoubtedly many more than a thousand larvae were para- 
sitized in each tray, but there is alwaj^s a certain amount of unavoid- 
able mortality of first-stage larvae in feeding trays. Many of the 
larvae are weak and do not get to the food and many are injured when 
the trays are cleaned and the larvae fed. 

SUCCESS OF COLONIES AND DISTRIBUTION OF A. MELANOSCELUS. 

Records of the success or establishment of colonies liberated and 
of the distribution of the parasite are obtained by collecting host 
material from the field and rearing the parasite from these larvae at 
the laboratory, or by collecting the cocoons of the parasite in the 
field. 



22 BULLETIN 1028, U. S. DEPAETMENT OF AGRICULTURE. 

Often the parasite is recovered the year following colonization. 
A. melanoscelus has been recovered from all but one of the colonies 
liberated previous to 1918. It has been recovered from half of the 
colonies put out in 1918 and from both of the colonies liberated in 
1919. Recoveries of the parasite were made late in the summer of 
1920 in a few of the towns which were colonized during June of that 
year. 

DISPERSION. 

The inner black line on the map (PI. IV) shows the present known 
distribution of the parasite in New England, it having been recovered 
from practically every town within this line. It is probable that in 
some cases A. melanoscelus has spread beyond the line indicated, for 
many of the towns just outside of the dispersion line have not been 
scouted. 

It is rather difficult to determine the exact distance the parasite 
will spread in a year, for when the parasite is scarce its recovery is 
largely a matter of chance. The number of host larvae which it is 
practical to collect in an endeavor to rear the parasite for disper- 
sion records is infinitesimal when compared with the larvse present 
in a town. Scouting for the cocoons is more satisfactory, but this 
is not infallible, and the fact that a town may have been scouted and 
no cocoons found does not prove that the parasite is not present. 

The recovery records show that the greatest spread of this species 
has been to the north and northeast, similar to the dispersion of the 
gipsy and brown-tail moths. The data obtained indicate a spread 
of about 25 miles a year in this direction. During the summer of 
1918 there were two recoveries made which because of their loca- 
tions are of special interest. One of these recoveries was made at 
Provincetown, which is 25 miles northeast of Harwich, where the 
nearest colony of A. melanoscelus was liberated in 1915. The other 
recovery was made on the island of Nantucket, which is 25 miles 
south of the Harwich colony. In 1915 a colony of A. melanoscelus 
was liberated in Middleboro, about 33 miles southwest of Prov- 
incetown. The colonies at Harwich and Middleboro were the only 
ones that had been liberated in that part of the State. These recov- 
ery records can not be taken as absolute proof of a flight of 25 miles 
for the insect, as it is possible that cocoons of the parasite were taken 
to Provincetown and Nantucket on cordwood or other material. This 
does.not seem likely, however, for the parasite was not recovered from 
any of the other towns in southeastern Massachusetts until 1919. The 
number of cocoons taken at Provincetown and Nantucket in 1918 
indicated that the parasite had been present in both places for 1 year 
at least. 



APANTELES MELANOSCELUS GIPSY-MOTH PARASITE. 23 

SECONDARY PARASITISM. 

Cocoons of the first generation are not, seriously attacked by sec- 
ondary insects. Small collections of cocoons of this generation are 
made each year over a considerable area and rarely are they para- 
sitized over 10 per cent ; more often not more than 2 or 3 per cent are 
killed by secondaries. 

Unfortunately it is a different story with the hibernating brood, 
for approximately 75 per cent are killed annually by native secondary 
insects and ants. This seriously handicaps the increase of A. melaii- 
oscelus. Among the insects which have been reared from the hibernat- 
ing cocoons are at least three Ichneumonidae, and members of the 
Pteromalidae, Elasmidae, Eurytomidae, Entedontidae, and Eupel- 
midae. In this complex there are secondary, tertiary, and possibly 
quaternary and quinquenary insects. An investigation of the life 
histories and host relationships of these insects has received consid- 
erable attention at the laboratorj^, but has not been completed. Some 
of these insects have several generations during the early fall and 
then hibernate within the cocoons of A. fnelanoscelus. 

THE VALUE OF A. MELANOSCELUS AS A GIPSY MOTH PARASITE. 

The problem of obtaining the actual percentage of parasitism of 
the gipsy moth by A. melanoscelus or by any of the other introduced 
parasites, except the egg parasites, is a difficult and complicated mat- 
ter involving many factors. Records at the Gipsy Moth Laboratory 
show that larvae picked promiscuously from tree trunks and foliage 
to-day may give 30 per cent parasitism, while to-morrow the same 
number of larvae, collected by the same individual, in the same man- 
ner, and in the same locality, may not even show the presence of the 
parasite. 

For a number of years collections of gipsy-moth larvae have been 
made daily through the entire larval period at Melrose and Stone- 
ham, in an attempt to learn the true status of the parasites in that 
section. Each collection contained 100 larvae all of the same stage. 
The collections of each stage were continued as long as that particular 
stage could be found, and collections of the next stage were started 
as soon as 100 larvae of the next stage could be found. As there is 
quite an overlapping of stages, there were very often two collections 
on the same date at the same place. All of the collections were kept 
separate and the larvae were fed in trays until all of the parasites 
had issued. The trays were examined each day and any parasites 
which issued were removed and recorded. Individual collections, con- 
taining 100 caterpillars each, gave from nothing to as high as 40 
per cent parasitism of second-stage gipsy-moth larvae for the spring 



24 BULLETIN 1028, V. S. DEPARTMENT OF AGRICULTURE, 

generation of the parasite. The records of parasitism secured from 
fourth-stage caterpillars which represent the second or summer gen- 
eration of A. lyvelanoscelU'S were about the same. 

The second and fourth stages of the gipsy-moth larvae usually 
showed the highest percentage of parasitism, but a considerable num- 
ber of the individuals of the other stages were killed by the parasite. 
Occasionally collections were made which gave as high as 15 per cent 
parasitism, for each of the other larval stages. In large collections 
of larvae where all the caterpillars in sight were collected, the parasit- 
ism obtained averaged around 10 per cent for each generation. The 
collections from which these figures were secured contained from 
5,000 to 20,000 larvae. 

The figures obtained from the foregoing collections should not be 
taken as representing the value of the parasite. 

There are a great many parasitized gipsy-moth larvae which die 
in the field before the parasite maggot has had time to develop. The 
parasitized larvae do not eat so much as nonparasitized larvae and are 
inclined to crawl to out-of-the-way places and often are not seen 
by the collector. On the other hand, if one should search for the 
hidden larvae the collection would not be representative of conditions 
as they truly exist. 

There is each year a high percentage of mortality of the gipsy 
moth, which occurs whether insect parasites are present or not. This 
mortality varies from year to year depending upon the conditions 
which influence the contributing factors, but the average percentage 
of mortality (barring insect parasites) for any period of years is the 
same as for any other similar period of yeai^s, if the periods include 
a sufficient number of years to make the average a fair one. This 
average mortality is not sufficient to prevent the increase of the 
gipsy moth, nor is the parasitism by A. melanoscelus great enough 
to prevent the increase of this pest. Although the exact percentage 
of parasitism of the gipsy moth by this parasite can not be stated, it 
is evident that it has a very important place as a part of the sequence 
of parasites which in conjunction with the other natural agencies 
retards the increase of this injurious insect, 

ABUNDANCE OF A. MELANOSCELUS IN NEW ENGLAND. 

Apcmteles 7nelanoscelus, like some of the other introduced parasites 
of the gipsy moth, is found abundantly in rather small areas. Each 
year since the parasite has been established these areas of abundance 
have been found more often and over considerably more territory. 
Until the summer of 1916 the parasite was not found in any appre- 
ciable numbers excepting at local points in and around Melrose High- 
lands. During the summer of that year a location at Beverly, Mass., 
was found where A. melanoscelus was very common. During the 



APANTELES MELANOSCELUS GIPSY-MOTH PARASITE. 25 

same summer some interesting data were obtained from a medium- 
sized oak tree near the Gipsy Moth Laboratory at Melrose Highlands. 
This tree had many gipsy-moth egg clusters on it which had not been 
creosoted during the winter, so that on this particular tree there 
was a much heavier infestation of gipsy-moth larvae than on any of 
the other trees in the vicinity. As the summer progressed, cocoons 
of A. melanoscelus began to appear in surprisingly large numbers. 
WTien most of the first-generation maggots had issued and spun their 
cocoons, the underside of nearly every crotch on the tree was covered 
with Apanteles cocoons (PI. II, C). 

There were 5,140 first-generation cocoons collected from this tree. 
A few cocoons could not be reached and some had blown away before 
the collection was made. Later in the season 511 second-generation 
cocoons were taken from the tree, making a total of 5,651 cocoons of 
A. melanoscelus removed from this tree. Although heavily infested 
the foliage on the tree was not damaged much by the feeding of the 
gipsy moth larvse and very few gipsy-moth pupse were found on the 
tree. These data are not given as a sample of the condition of the 
trees in Melrose Highlands in 1916, but the figures are interesting 
and show what happens under some conditions. Occasionally large 
oak trees have been seen in other towns on which it was estimated 
there were from 6,000 to 10,000 cocoons. 

In 1918 this parasite was found in large numbers over an area of 
several acres of woodland in Cohasset, In 1919 and 1920 it was 
found abundantly in small areas in Hampton, N. H., and in the 
following towns in Massachusetts: Beverly, Quincy, Weymouth, 
Cohasset, Scituate, Marshfield, and West Boylston. 

CONCLUSION. 

Apanteles melanoscelus has been present in New England since 
1911 and is now firmly established. It is spreading rapidly from 
the colonies which have been liberated and is increasing in spite of 
its being heavily parasitized by secondaries. 

The fact that A. melanoscelus is able to complete its life cycle on 
several native insects adds considerably to its value as an introduced 
parasite and makes its permanent establishment more certain than 
if the gipsy moth were its only host. 

This parasite has two generations each j'ear on the gipsj^ moth 
and is very abundant in many small areas. It gives promise of 
becoming one of the most valuable of the imported parasites. 



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